DIVERSITY OF FRESHWATER FISH AND CRUSTACEANS OF ST. THOMAS
WATERSHEDS AND ITS RELATIONSHIP TO WATER QUALITY AS AFFECTED
BY RESIDENTIAL AND COMMERCIAL DEVELOPMENT

WRRI Project 2006VI73B

Prepared by:

Donna Nemeth
Renata Platenberg

July 2007

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

DISCLAIMER

The research on which this report is based was financed in part by the U. S. Department of
the Interior, United States Geological Survey, through the Virgin Islands Water Resources
Research Institute. The contents of this publication do not necessarily reflect the views and
policies of the U. S. Department of the Interior, nor does mention of trade names or
commercial products constitute lthir endorsement by the United States Government.

Diversity of freshwater fauna in St. Thomas gut streams

ABSTRACT

In the US Virgin Islands there has been considerable effort in surveying and mapping
watersheds and riparian corridors. However, there has been little previous effort to
document the freshwater systems, namely, the stormwater drainage guts. These guts form a
vital connection between terrestrial habitats and upland activities and the downstream
marine environment-yet research on the problems of non-point source pollution has largely
overlooked the watershed habitat through which these pollutants are transported. Upland
activities affect the levels of contaminants that flow through these habitats. We conducted a
study to assess the impacts of levels of watershed development on the diversity of
freshwater fauna. Three guts were selected that varied in development impact: Neltjeberg
(low impact), Dorothea (moderate impact), and Turpentine Run (high impact). Freshwater
habitats in a highly developed watershed contained more non-native fish species (guppies
and tilapia) compared to those with low to moderate levels of development. The least
impacted systems had higher native faunal diversity; Neltjeberg had 7 species of native
shrimp and fish, compared to 5 in Dorothea and 4 in Turpentine Run. Total Phosphorous
levels were highest in the most developed watershed (1.3-1.5, vs. 0.8-1.2 mg/L), and both
Total Phosphorous and Total Kjeldahl Nitrogen were elevated downstream of a residential
sewage input (TP 0.14-0.41 mg/L vs. 0.02-0.10 mg/L in upstream pool; TKN 2.36-2.44
mg/L vs. 1.10-1.21 mg/L in upstream pool). Other water quality parameters, including
temperature, pH, and salinity did not show any pattern consistent with level of development.
Island development may impact tropical streams with regard to excessive nutrient input and
introduction of exotic species. The amphidromous lifecycle of native shrimps and fishes
and its effect on stream colonization are likely to increase natural variability to the animal
community present in gut streams. This could serve to protect streams against permanent
loss of species if conditions were to become uninhabitable at any given time.

Table 1 Access points to St. Thomas guts surveyed in this study 5
Table 2 Dates of data collection at the three guts 7
Table 3 Size of gut pools surveyed at each site on sampling occasion 10
Table 4 Presence of species sampled in low, moderate, and high impact guts 15
Table 5 Total Kjeldahl Nitrogen and Total Phosphorous levels in three gut 18
streams on two dates
Table 6 Average water quality parameters 18

Diversity of freshwater fauna in St. Thomas gut streams

INTRODUCTION

Background

There has been considerable effort in the US Virgin Islands (USVI) to document and map
watersheds and wetlands (e.g., Knowles and Amrani, 1991; Stengel, 1998; Island Resources
Foundation, 2004; Platenberg, 2006). St. Thomas has limited natural freshwater resources,
represented by man-made agricultural ponds and a small number of riparian stormwater
corridors known locally as "guts". Prior to this study, there had been little work
documenting the species composition and its variation among different guts.

On St. Thomas, the terrain is characterized by steep hillsides with thin soils and a low
permeability of underlying rock. As such, rainfall tends to run down hillsides over the
surface through gut channels (Jarecki and Walkey, 2006). Native plant communities along
these guts are more mesic than the surrounding upland vegetation, despite that the majority
of these guts carry water only seasonally, and flows vary dramatically with rainfall levels.
Several species of freshwater fishes and shrimps have been observed to persist in these
habitats (Loftus, 2003; pers. obs.). Non-native species of invertebrates, fish, and amphibians
are also prevalent.

The demands for space by a rapidly growing human population of over 100,000 in the USVI
have resulted in extensive loss and degradation of natural ecosystems, especially on densely
populated St. Thomas. Upland development activities are taking place in an unprecedented
manner, resulting in increases in unregulated sediment runoff, in addition to agricultural and
road runoff and other sources of contamination.

The guts are the primary channel for moving sediment and non-point source pollution
resulting from upland activities into lowland wetlands and the marine environment
(Platenberg, 2006). These contaminants have a significant negative impact on the coral reefs
and fisheries resources that serve as the backbone of the USVI economy (Division of Fish
and Wildlife, 2005). Despite this, there has been little attention paid to the effect of such
contaminants on the aquatic species contained within, or the ecological function of, these
conduit systems. The freshwater shrimp have a role in reducing sediment in streams (Pringle
et al., 1999), and they are particularly vulnerable to anthropogenic activities (Garcia and
Hemphill, 2002). It may be that these species and associated communities provide a valuable
role as bioindicators of the health of these systems.

Island setting

Situated near the eastern terminus of the Greater Antillean chain of islands in the northern
Caribbean Sea, the USVI comprise four major inhabited islands and more than 50 smaller
offshore cays. St. Thomas, St. John, and Water Island are the three main northern islands,
located on the Puerto Rican Shelf to the east of Puerto Rico, while St. Croix is on a separate

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

shelf to the south. The islands are mostly volcanic in origin, with steep slopes and irregular
coastlines. The terrain is characterized by these steep hillsides with thin soils and a low
permeability of underlying rock (Jarecki, 2003). The highest elevation is on St. Thomas (474
m), with highest points on St. John, St. Croix, and Water Island being 395 m, 355 m, and
91m, respectively. St. Thomas has an area of approximately 7861 ha, and is the most
densely populated of the islands (USDA-NRCS, 1998). The islands are surrounded by coral
reefs and seagrass beds.

The climate of the islands is dominated by easterly tradewinds, with poorly defined seasonal
variation in rainfall. December/January to April are generally dry months, while May
through November are considered wet months. Rainfall is frequently highly localized, with
the more mountainous north side of St. Thomas receiving more rainfall than the flatter
eastern end.

Guts in the US Virgin Islands

In the USVI rainfall tends to run downhill over the surface rather than through the ground
because of the thin soil layer and impermeability of underlying rock. The natural channels
S t -. formed are from this storm water
erosion down steep slopes are locally
referred to as guts, and are defined as
any stream with a well-defined channel
h. a n including those that result from an
Accumulation of water after rainfall. A
typical gut is a narrow channel,
generally between 1-4 m wide, with a
loose rocky or boulder substrate and
devoid of understory vegetation (Figure
1). Vegetation communities in guts
consist of corridors of mesic vegetation,
including broadleafed evergreen trees
and wetland herbaceous species such as
papyrus Cyperus spp. and sedges Carex
spp. (Thomas and Devine, 2005;
Platenberg, 2006).

Natural springs are generally located in
guts, resulting in reliably permanent
pools of freshwater. Gut pools provide a
rare opportunity for freshwater
resources in the USVI, where natural
freshwater ponds are lacking. These
pools provide habitat for a number of
species, including wetland and
Figure 1. Typical gut drainage on St. Thomas. Note migratory birds, freshwater shrimp and
the absence of vegetative understory, bouldery
substrate, and lack of water. Guts fill with water after
a significant rainfall event.

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

fish, and amphibians. Historically, guts have been dammed to provide available water for
crop irrigation, particularly during the plantation era. Intermittent streams are often
supplemented from gray water discharge in residential areas. Only a few of these guts have a
direct connection to the marine environment except during storm-induced discharge.

Guts are protected under local regulations (VI Code, Title 12, Chapter 3: Trees and
vegetation adjacent to watercourses) that prohibit the cutting or injury of any tree or
vegetation within 30 feet of the center or 25 feet from the edge of the watercourse.
Additional protection is afforded from efforts to reduce non-point source pollution by the VI
divisions of Environmental Protection and Coastal Zone Management.

Rainfall, runoff, and sedimentation

Sediment poses a serious threat to wetlands and the marine environment in the USVI.
Construction on hillsides loosens and exposes soils that are carried by runoff water through
guts into salt ponds and bays (Ramos-Sharr6n and MacDonald, 2005). Sedimentation occurs
when soil is eroded from the land surface and is collected and delivered to drainages by
rainfall moving over the surface of the ground. Sediment yields on St. John have
significantly increased since the 1950s as a result of erosion from unpaved roads
(MacDonald et al., 1997; Ramos-Sharr6n and MacDonald, 2005).

Rainfall runoff also collects other contaminants from human activities, including pesticides,
nutrients, and toxic substances, resulting in non-point source pollution. Leaky septic systems
(or direct discharge of sewage) and runoff from animal operations result in high loads of
bacterial contamination in gut streams, a main cause of beach contamination after significant
rainfall events (Division of Environmental Protection, 2004). In the USVI municipal trash
collection dumpsters are located on major roads, often where the guts transect the roads.
Wayward trash invariably ends up down in the guts and can be carried directly to the sea in
major rainfall events.

The role of guts in the transport of these contaminants to salt ponds, mangroves, and marine
environments has been largely overlooked. Sedimentation and contaminants have a severe
detrimental effect on the high economically valuable marine resources for tourism and
fisheries, and as such the Coastal Zone Management program has strict guidelines to
regulate activities occurring in coastal areas in order to protect critical wetland resources. In
the USVI, upland activities in the USVI are not included in this program due to a two-tiered
system for permitting. This results in unregulated activities that directly impact these critical
resources via the guts. There has as yet been no attempt to quantify this impact (Platenberg,
2006).

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

Overview of impact assessment

We examined three parameters to determine impact of residential and commercial
development on gut function: the physical characteristics of gut pools, diversity of
freshwater fauna, and chemical characteristics of the water.

Goals and objectives of study

The primary objectives of this study were to:

Determine if three St. Thomas gut streams varied in water quality and if that
correlated with the level of human impact in the surrounding watersheds.
Identify all aquatic species found in the gut stream habitats and look for distribution
patterns with respect to among-gut differences in water quality and human impact.

We tested the null hypothesis that watershed development had no effect on the diversity of
fish and shrimp species present.

METHODOLOGY

Watershed and gut selection

Watersheds exhibiting low, moderate, and high disturbance from residential and commercial
development were identified using criteria for assessing impairment of watersheds (Island
Resources Foundation, 2004). These criteria include percentage of watershed with impairing
land uses, presence, condition, and width of wetland buffers, hydrological alteration,
vegetation removal, and pollution. Data on these criteria are largely lacking for gut systems,
and therefore we conducted site visits to several guts to assess impairment. Guts were also
selected for presence of permanent gut pools as available habitat for fish and shrimp. The
guts selected for this study are shown in Figure 2 and access to them described in Table 1.
Notes on relative water flow and stream condition (clarity, sediment) were qualitatively
described. Tree canopy prevented georeference of individual pools.

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

Neltjeberg Gut /
Dorothea Gut Turpentine Run
Turpentine Run
| Watershed Boundaries
SDeveloped Areas
0 2 4 8 Kilometers
I I I I I I I I I

Figure 2. Map of St. Thomas showing the three guts surveyed. Approximate location of
pools surveyed is indicated by the arrowhead.

Objectives: to identify all aquatic species using the gut stream habitat, and to look for
patterns with respect to differences in water quality and land development.

Fish and shrimp were sampled using small aquarium nets, with the observer slowly turning
over each rock in the pool to look for shrimp (especially Macrobrachium spp.) hiding

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

underneath. Shrimp size and presence of eggs on the abdomen were noted to provide insight
into the life history stages present at the various sampling dates. A representative sample of
shrimps was collected live and identified using Chase and Hobbs (1969). Subsets of these
were preserved as a reference collection (Appendix 1). We recorded the presence of
tadpoles, snails, and aquatic insects in the pools, and also opportunistically recorded species
that we saw in other pools along the gut.

On one occasion (3 June 2006), plastic funnel traps (minnow traps, baited with canned
catfood) were set overnight in the Dorothea gut. The traps captured only a subset of the
shrimp species that were visible in the pool, and thus we decided to rely on visual sampling
and hand collection of individual organisms for confirmation of their identity.

Water Testing

Objectives: to determine if the gut streams varied in measurements of water quality, and to
determine if those parameters varied with respect to our categories of 'low', 'medium', and
'high' relative development.

Nitrogen, Phosphorous, and E. coli
Total Kjeldahl Nitrogen (TKN), Total Phosphorous (TP), and the presence of E. coli in the
stream water were evaluated on two different dates for all three guts. Water samples were
collected in 500ml Nalgene bottles, stored in a cooler on ice, and transported to UVI. Water
samples to be evaluated for TKN and TP were stabilized by the addition of lml sulfuric
acid/500 ml water and refrigerated at 40C. TKN and TP tests were performed UVI's Center
for Marine and Environmental Studies using EPA method 351.2 (TKN) and EPA method
365.4 (TP).

The presence of coliform bacteria was determined with an EPA-approved test (Readycult,
available from Merck). This chromogenic enzyme substrate method uses the X-GAL
chromogen for detection of the total coliform enzyme (B-D-galactosidase). The presence of
E. coli specifically was tested for with the addition of Bactident Indole Reagent.

In the Dorothea gut, we identified an input of residential sewage that an area resident (Mark
Gordon, pers. comm.) said came from a house that had become disconnected from the
community septic system. In that gut, we sampled water for TKN, TP, and E. coli from
pools 20m upstream, and about 20 m and 50m downstream of the sewage input.

To look at daily fluctuations in several water
quality parameters, we deployed a YSI water -
quality meter/data logger system in one of the me.
upper Neltjeberg gut pools March 10-13, 2007.
The data logger recorded temperature, pH, total .
dissolved solids, turbidity, nitrate-nitrogen, and
dissolved oxygen.

Rainfall
Rainfall data was acquired and summarized
from a weather station located at the top of
Crown Mountain (18 21 29 N, 64 o 58 21 "
W; elevation 421m, St Thomas, VI). Data are
available from Weather Underground website at
http://www. wunderground.com/weatherstation/
WXDailyHistory.asp?ID=KVISTTHO 1.

Figure 3. Water quality parameters were
RESULTS measured using a hand-held meter.

Watershed and gut selection

We surveyed the three guts over a nine-month period (May 2006 to February 2007). Data
were collected on three dates per gut, in summer, fall, and winter (Table 2).

Neltjeberg (Low Impact)
Neltjeberg Bay is located within the Dorothea watershed (Figure 2, above) in a drainage
basin with very low density residential development on the north side of St. Thomas. Three
guts drain into Neltjeberg Bay. The easternmost gut, which we sampled, contains a spring
and therefore has permanent pools, some of which are several meters across and at least 0.5
m deep (Table 3). Along the segment of the gut surveyed, there is no human encroachment
except at the access along a culverted estate road (Figure 4).

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Diversity of freshwater fauna in St. Thomas gut streams

During our study, land-clearing and new
construction was initiated in the Neltjeberg
gut, which may have made it more 'impacted'
than our initial designation would lead us to
believe. During creation of new driveways,
topsoil was dumped directly into the gut
(Figure 5) and we saw significant changes in
the amount of suspended and benthic sediment
in the gut pools after October 2006-
especially after heavy rainfall, the stream
water was milky brown (Figure 6) making it
nearly impossible to visually survey for
animals. By February 2007, there was
noticeable algal growth and a thick sludge
covering bottom in pools.

Figure 4. Representative view of Neltjeberg Gut

Figure 5. Habitat destruction in
gut as a result of bulldozing

Figure 6. Increased sediment in gut as a result of upland
bulldozing activities

Dorothea (Moderate Impact)
Dorothea Bay is located within the Dorothea watershed in a drainage basin with medium
density residential development and agricultural use (Figure 2, above). One major gut drains
into the bay; this gut has a persistent stream flow and several large, deep pools (Figure 7;
Table 3) with shrimp and fish. Several human encroachments impact the gut along the

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Diversity of freshwater fauna in St. Thomas gut streams

segment surveyed, including residences with altered vegetation, residential water extraction,
a direct sewage input, and a concrete bridge and culvert that spans the watercourse.

One of the most noticeable impacts of human activity on the freshwater community was
observed downstream of a residential sewage discharge (Figure 8). Upstream, pool substrate
was composed of sand and small rocks, and walking over the substrate did not cloud the
water in the pool. Whole leaves were present, but there was almost no fine sediment
present. Over 20m downstream of the sewage input, one pool bottom was covered in thick
fine mud (over 15cm deep), which released gases from anaerobic bacterial activity and
clouds of fine sediment when disturbed. Downstream of the discharge, the pool substrate
changed from gravel, to a thick layer of anoxic sludge. The downstream pools were also
affected in terms of nutrient load (increased) and native fauna (decreased; see sections
below).

I

a

Figure 7. Representative view of Dorothea Gut

Figure 8. Sewage input in Dorothea gut
(yellow arrow)

Turpentine Run (High Impact)
This gut is located within the highly developed Jersey Bay watershed on the eastern side of
St. Thomas (Figure 2, above). Turpentine Run is the only perennial stream on St. Thomas,
although its flow is augmented by water treatment effluent and channelization (Figure 9).
Compared to the other two guts, this stream was broader and the pools of much larger

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Diversity of freshwater fauna in St. Thomas gut streams

volume (Table 3). Intense development in ,
the upper drainage basin has created m.
significant impervious surfaces resulting in
increased runoff and channel flow through
this gut. Increased sediment loads add to
the input of often-polluted water that flows
through this channel. Turpentine Run was
so polluted at one point that it was
designated as an Environmental Protection
Agency Superfund site. Since the mid-
1990s a major cleanup effort has been
underway resulting in a decline in direct
contamination from petroleum storage and
dry cleaning operations, with treated
groundwater being discharged directly into
the gut (http://www.dpnr.gov.vi/de/
superfund_ program.htm). This has resulted
in a steady and often strong stream flow.
Although there was no direct human
encroachment along the section surveyed,
which is below the discharge input, there
were considerable levels of trash in and
along the stream.
Figure 9. Representative view of Turpentine Run

A total of five species of shrimp and four species of fish were located during our survey.
Descriptions and an identification guide to shrimp species are provided below, as well as
their presence in the three guts (Table 4).

Figures and descriptions below are modified from Chase and Hobbs (1969). This reference
includes excellent keys to identification of freshwater crustaceans of the West Indies.
Figure 10 is provided as an aid to crustacean anatomical terms.

Three genera of shrimp from the families Palaemonidae (Macrobrachium) and Atyidae
(Atya and Xiphocaris) were collected, comprising a total of five species.

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Diversity of freshwater fauna in St. Thomas gut streams

Macrobrachium
The genus Macrobrachium contains large predatory shrimp that were predominantly found
hiding under rocks during the day. We rarely found more than one individual ofM. carcinus
per gut pool, which is consistent with previous reports that they are territorial and
aggressive. During our daytime surveys, often the only evidence that they were present was
a freshly molted exoskeleton.

M. carcinus (Figures 11 and 12) can reach a postorbital carapace length of more than 90mm,
making it the largest shrimp species found locally. It is distinguished by its elongate claws
(second periopods) which are similar in size, and cross at the tips when closed. The carpus
is about half as long as the palm, and shorter than the merus. The movable dactyl of the
claw has a white spot visible at its base when the claw is open. Both the fixed claw and
movable dactyl are armed with a large tooth near midlength (dactyl) or slightly more
proximal (fixed finger). The rostrum is dorsally armed with 11-16 teeth. Color varies from
blue black to brown, often with longitudinal dark and light stripes on carapace and abdomen.

M. faustinum (Figures 13 and 14) was more frequently encountered. Generally we found
this species by turning over rocks, but the smaller individuals were often moving around the
pool in the open. M. faustinum reaches a maximum postorbital carapace length of about 18
mm. It is distinguished from M. carcinus in having its second periopods unequal in size.
The palm is covered with a soft dense fur, and the fingers of the second periopod show a
conspicuous light and dark banding pattern. These bands are visible even in very small
individuals that may not yet show a great difference in the shape or size of the two second
pereiopods. Juveniles also have the proximal segments of the second and third pereiopods
deeply pigmented. The carpus is as long or slightly longer than the palm, and longer than
the merus. The rostrum is dorsally armed with 13-15 teeth. Color is a translucent tan, and
most individuals show a U-shaped cream-colored bar on the third abdominal tergum.

Atya
Atya is distinguished from other St. Thomas shrimps by having the chelae of first and
second pereiopods with tufts of long hairs, used in filter-feeding or for 'mopping' the
substrate for organic particles (Figures 15 and 16). The hairs can be seen when viewing the
shrimp in a clear container of water; in an aquarium, they orient the pereiopods into the
water current like a baseball catcher's mitt. The rostrum is unarmed dorsally. A. lanipes
(Figure 16) has a maximum postorbital carapace length of 28mm. Color is light to dark
brown, with the dorsal surface often with a longitudinal darker brown stripe extending from
carapace onto abdomen.

A. innocous (Figure 15) is distinct from A. lanipes in having the third pereiopods bearing
prominent horny tubercles (lacking in A. lanipes) and considerably larger and more robust
than the fourth pereiopod (only slightly larger in A. lanipes). Its maximum postorbital
carapace length is 34 mm.

Xiphocaris elongata (Figure 17) are a small, slender shrimp often visible swimming in
midwater. This species lacks the tufts of hair on the fingers of the chelae of first and second
pereiopods (as seen in Atya). When netted and lifted out of the water, they actively flexed
their abdomens and often flipped themselves out of the net. Maximum size is about 15 mm
postorbital carapace length. The rostrum is long and conspicuous (0.8-1.3 times carapace
length), with a finely serrated ventral margin. Color is translucent green, with internal
organs visible through the carapace.

/ '
....

/

Figure 17. Xiphocaris elongata (figure from Chase
and Hobbs, 1969).

Fish
Two species of native fish and two non-native species were identified.

The Sirajo Goby (Sicydium plumieri) reaches a maximum total length of 7.5-10 cm
(Mowbray, 2004), but the maximum size we collected was less than 5cm. Males in breeding
coloration are iridescent blue (Figure 18), otherwise individuals are light gray in color. The
pelvic fins are fused into a modified suction cup in the characteristic gobiid form, to assist
the fish in holding its position on the benthos in flowing water. The Sirajo goby grazes on
benthic algae. It is an amphidromous species, with a marine larval phase. They were
observed in pools with strong water flow, and we saw up to six individuals in a single pool.

The Mountain mullet (Agonostoma monticola, Figure 18), another amphidromous species,
can reach a total length of 21 cm (Mowbray, 2004). We observed them in groups of up to
six individuals per pool, with the largest individual less than 12cm. Mountain mullet are
omnivorous, and in captivity were observed to consume guppies and juvenile shrimp. They
also struck at and killed shrimps that were too large for them to swallow.

Guppies (Poecilia reticulata, Figure 18) are native to Trinidad, but are common on many
Caribbean islands where they were likely introduced for mosquito control.

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Diversity of freshwater fauna in St. Thomas gut streams

Tilapia (most likely Oreochromis sp.) are African natives that have become widespread
throughout the Caribbean where introduced for aquaculture. Although they can survive in
seawater, we are unaware of any records of them in the sea surrounding St. Thomas and thus
they are likely restricted to the streams where they were introduced.

Neltjeberg (low impact)
Neltjeberg, the 'low impact' gut, had five species of native shrimps and two native fish
species, with no introduced species (Table 4). Neltjeberg was the only gut that contained all
the native species found to date on St. Thomas. In Neltjeberg, only 1 individual Atya
innocous was observed, in June 2006. No other individuals were found on subsequent visits
in July & October 2006 and February 2007. Atya lanipes shrimp were found bearing eggs on
the abdomen in Neltjeberg in July 2007, but not on visits in October 2006 or February 2007.

Dorothea (moderate impact)
Dorothea had four shrimp species, plus the native Sirajo goby and introduced guppies. In
Dorothea, a number of ovigerous shrimp species were seen in September 2006:
Macrobrachium faustinum, Atya lanipes (8-11mm postorbital carapace length); Xiphocaris
elongate (11-14mm postorbital carapace length). No shrimp were observed with eggs in
October 2006 or January 2007. Male Sirajo gobies were observed in bright blue breeding
coloration in September 2006. Other species observed included Coqui frogs
(Eleutherodactylus coqui), Cuban treefrogs (Osteopilus septentrionalis), the terrestrial
soldier crab (Coenobita clypeatus), green iguana (Iguana iguana), and dragonfly larvae.

The input of untreated sewage in Dorothea gut was associated with a dramatic change in the
fish and shrimp community. Directly upstream of the sewage discharge, gut pools contained
4 species of shrimp (Macrobrachium carcinus, M. faustinum, Xiphocaris elongata, and Atya
lanipes) as well as the Sycidium goby and guppies. Downstream of the discharge, native
species of shrimp and fish were absent, with only introduced guppies and Malaysian trumpet
snails persisting.

Turpentine Run (high impact)
Turpentine Run had three shrimp species (no Atya), the native mountain mullet and two
introduced species, guppies and tilapia. In Turpentine Run, Tilapia were observed, and
many were constructing depressions in the sand for nesting, in July of 2006. No tilapia were
observed on later visits in fall 2006 and winter 2007. None of the shrimps collected in
Turpentine Run were observed to be bearing eggs (June, October 2006; Feb. 2007).

Nitrogen, Phosphorous, and E. coli
Total Kjeldahl Nitrogen (TKN) and Total Phosphorous (TP) were the only water quality
parameters measured that showed an association with human activity. Total Phosphorous
concentration was more than four times higher in the most developed watershed (Turpentine
Run, 0.17mg/L(Oct) and 0.22mg/L(Feb), Figure 19; Table 5) relative to the least developed
gut (Neltjeberg, Omg/L(Oct) and 0.05mg/L(Feb). Dorothea (medium development) had
intermediate levels of TP. In Dorothea gut, the residential sewage discharge provided a
reference point for comparison of conditions upstream and downstream of this human
impact. Total Phosphorous increased four- to seven-fold at the site of contamination

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Diversity of freshwater fauna in St. Thomas gut streams

(0.14mg/L(Oct), 0.41mg/L(Feb)) relative
0.10mg/L(Feb))(Figure 20).

to upstream conditions

(0.02mg/L(Oct),

05

04

. 03
0~0-

01-
-.

Neltjeberg

Dorothea

Turpentine Run

Figure 19. Total Phosphorous in three gut
streams in St. Thomas on two sampling dates.
Grey indicates October 2006, black February
2007

TKN actually decreased slightly with level of development, ranging from 1.28-1.49 mg/L in
Neltjeberg (least developed) to 0.84-0.95 mg/L in Turpentine Run (highly developed)
(Figure 21; Table 5). However, in Dorothea gut, the residential sewage discharge was
associated with TKN levels that more than doubled, from 0.02-0.10 mg/L to 1.1-1.2mg/L
downstream of the discharge (Figure 22).

3 3

25

S2

S15

-1

05

0 -

25

2
0J
15
z
1

05

Neltjeberg Dorothea Turpentine Run

Figure 21. Total Kjeldahl Nitrogen in three gut streams
in St. Thomas on two sampling dates. Grey indicates
October 2006, black February 2007.

E. coli was present in all three streams in October 2006 and February 2007.

Water Quality Characteristics
We did not observe any clear differences between the three streams in terms of their
temperature, pH, total dissolved solids, conductivity, or salinity. The range and means for
water quality parameters for each stream are pooled and shown in Table 6. The data were
not statistically compared because we realized that we had not standardized the time of day
when the readings were taken, and it became evident that several parameters varied
substantially over the time of day. No clear seasonal pattern was seen for pH in the guts
(Figure 23). The low pH for Neltjeberg in summer may have been an artifact due to
inaccurate meter calibration.

Figure 23. Mean pH of gut stream pools was variable and showed no consistent trends
among season or site (n=5 pools per stream, except for Neltjeberg fall (n=1). Error bars
indicate 2 standard deviations from the mean (approximate 95% Cl).

Data from the YSI water quality meter/data logger allowed us to look at variation in water
quality parameters over a three day period. Temperature and dissolved oxygen showed
daily cycles, increasing mid-day and falling at night; turbidity showed the reverse, with
highest turbidity recorded at midnight (Figure 24). pH was somewhat cyclical with higher
mid-day values, yet showed a lot of variability over the 3-day period (mean pH 7.74+0.08,
range 7.54-7.89). Nitrate-Nitrogen also showed a daily cycle, tending to be higher mid-day
(Figure 25) (mean 8.050.38 mg/1). Where TKN includes ammonia plus organic nitrogen,
Nitrate-Nitrogen measures a different form of inorganic nitrogen.

Neltjeberg Gut

1 84

1 82

180
3-
S1 78
0
S1 76

1 74

1 72

1 70

120

100

80

60 O

40

20

0

105 110 115 120 125 130 135

Date (March 2007)
Figure 24. Water quality parameters from a YSI water quality meter/data logger system in one of the upper
Neltjeberg gut pools March 10-14, 2007. A date of'10.5' indicates a time of noon on March 10, '11.0' indicates
midnight of March 10, etc.

Diversity of freshwater fauna in St. Thomas gut streams

Neltjeberg Gut Nitrate-Nitrogen levels over 3 day
period (10-13 March 2007)

Figure 25. Nitrate-Nitrogen readings from a YSI water quality meter/data logger system in one
of the upper Neltjeberg gut pools March 10-14, 2007. The first time of "12:00:40" refers to noon
on March 10; remaining times are listed as 12 hour intervals from that start time.

Rainfall
The Virgin Islands experience two rainy periods during the year, in April- May and again in
October-November. February and March are typically the driest months. Average annual
rainfall in St. Thomas is 97.4 cm. (http://www.vinow.com/usvi/weather.php#rain).

In October, the heavy rains (Figure 26) were associated with slightly greater water flow in
the three guts. In Turpentine Run, we saw evidence of flash flooding-papyrus plants along
stream margin were flattened against the banks, and we could see where the water flow has
come up the banks at least 50cm vertically in some areas (Figure 27). In Turpentine Run,
the water was foamy, and brown with suspended sediment.

We tested the null hypothesis that watershed development had no effect on the diversity of
fish and shrimp species present. Although our observations are limited in scope both along
each watershed and in number of sampling dates, we see several trends that support our
hypothesis and suggest further study.

Organic pollutants were the most informative in terms of correlating water quality
with the human impact. According to the U.S. Environmental Protection Agency
(http://www.epa.gov/waterscience/criteria/nutrient/), "Nutrients, nitrogen and phosphorus,
have consistently ranked as one of the top three causes of use impairment in US waters for
more than a decade." Sources of these organic compounds can include human and animal
waste, or fertilizers, which are likely to enter gut streams in areas where sewage treatment is
absent or poorly maintained, or in areas where there is heavy agricultural activity. Excess
Phosphorous and Nitrogen can negatively impact freshwater habitats through their
promotion of harmful algal growth and subsequent hypoxia as the algae decompose.

Total Phosphorous levels increased with relative amount of watershed development.
Turpentine Run receives effluent from a number of commercial businesses in the Tutu area
of St. Thomas, including laundries, which could account for high phosphorous input. Both
TP and TKN increased downstream of a residential sewage input in Dorothea gut. This input

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

of organic material resulted in the accumulation of fine sediments where anaerobic bacteria
and blue-green algae thrived; no shrimp or gobies were observed in this area despite their
persistence in the pools upstream throughout the duration of our study. Atyid shrimps (Ayta
and Xiphocaris) have been shown to reduce sediment loads in stream pools (Pringle et al.,
1993). Thus, if they are unable to inhabit, or avoid, pools with high organic pollution, such
streams may lack natural controls to reduce the impact of added nutrients. The presence of
the introduced guppies and trumpet snails in the polluted pools may reflect a greater
tolerance of environmental conditions by such species. The population density of these
exotics was dramatically higher (thousands of individuals in pools less than a meter
diameter) in the polluted pools relative to other areas where they were observed. Malaysian
trumpet snails feed on algae and dead plant material, but avoid other live plants (Avila,
2007) -thus, they may actually mitigate some of the impacts of pollution.

The U.S. Environmental Protection Agency website (http://oaspub.epa.gov/
nutdb/reports.control, 2006) provides water quality criteria by state/ecoregion, and we found
average values for TKN and TP for a number of Puerto Rico counties, which we provide to
give some relevant context to our measurements. Over all the counties, TKN ranged from
0.05 to 5.27 mg/L (mean: 0.50mg, N=494 observations-compare to our data, where TKN
ranged from 0.8-2.4 mg/L); TP ranged from 0.0025 to 2.4 mg/L (mean: 0.16 mg/L, N=585
observations-compare to our data, where TP ranged from 0.0-0.4 mg/L).

The presence of E. coli in the streams could result from either human or animal waste
contamination. Its presence in all three guts likely results from lack of proper sewage
treatment and containment in residential systems, as well as proximity of livestock to the
streams.

Streams with the greatest level of development had fewer fish and shrimp species.
Non-point source pollution or the introduction of other contaminants could reduce the
habitability of the other two streams for certain native species. Our observations that the
habitat downstream of a residential sewage leak was severely modified in nutrient load, had
heavy sediment accumulation, and lacked native species in pools immediately downstream,
provided the clearest support for the potential impact of nutrient loading. The only species
present in those areas were guppies, and an introduced Malaysian trumpet snail (Melanoides
tuberculata) that feeds on dead and decaying organic matter. Atyid shrimps (Atya and
Xiphocaris) are known to significantly reduce the accumulation of benthic sediments, which
affects community structure through allowing higher biomass of algae and benthic insects
(Pringle et al., 1993). Thus, the absence of such species can have a major impact on the
entire community food web structure.

Human activity can also impact the ability of native species to colonize streams and
maintain stable populations. We had heard of one example in which landowners had filled
estuarine pools with soil, supposedly to reduce mosquito breeding populations. However,
this also effectively interrupted water flow between the gut and sea. Since all the native
shrimps and fish are amphidromous, this would also prevent the movement of eggs, larvae,
or juveniles between the freshwater and marine environments. Studies by Garcia and
Hemphill (2002) in Puerto Rico have expressed concern over the potentially devastating

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

effect humans can have on freshwater shrimp populations, through damming, loss of
estuarine nursery habitat from development and water contamination, and the effects of over
harvesting. A case study involving chemical poisoning of the Espiritu Santo River found
that Atya shrimp populations did not recover for 2 years due to lack of recruitment
(Greathouse et al., 2005).

Streams with the greatest level of development had introduced species present. The
presence of two non-native fish species in the mid and high impact guts also supports our
hypothesis that human impact can modify stream communities. Guppies, which were likely
introduced for mosquito control, would have been placed in streams near where humans
would encounter heavy mosquito populations. Tilapia have been brought to the VI for
aquaculture, and may have been accidentally or intentionally released in some streams and
ponds. Both fish species have the potential to prey on other native species and their larvae,
or to compete with them for food resources. Malaysian trumpet snails were present in all
three guts, and could have been introduced with imported aquatic plants.

Atya shrimps may be useful as a bioindicator in tropical freshwater streams. In our
study, the shrimps either actively avoided pools with high organic loads (TKN and TP) or
could not survive there. Shrimp do not tolerate low dissolved oxygen levels, which would
be a likely consequence of the high organic load. In addition, Atya was not found by us in
Turpentine Run-is its absence a consequence of higher phosphorous levels in that gut,
other chemical pollutants, or random colonization? More work is necessary to examine the
sensitivity of different species to pollutants and changes in water quality. Alternatively, the
introduction of Tilapia, potential predators, could reduce the ability of these shrimps to
successfully colonize or persist in that stream.

FUTURE RESEARCH DIRECTIONS

Future studies should account for seasonal variability in water flow and continuity of
the estuary. There is likely a component of chance as to what species may be found in a
given watershed, because all the native fish and shrimp species are amphidromous, with a
marine larval phase. Because of the high variability in rainfall and water flow throughout
the year, the guts do not always maintain access to the sea for larval shrimp or fish to enter
(personal observation). Thus, there is likely to be high natural variability in terms of a given
species finding a particular stream at the correct time in its larval development. The fact that
some species may migrate downstream to release eggs from a point closer to the sea (Bauer,
2004) could account for the apparent disappearance from some study pools in the autumn
and winter. Future studies should consider surveying the entire stream more extensively
along its length to address population variation associated with migrations associated with
reproduction and colonization.

We recognize that there are many other potentially productive research questions that
remain to be addressed regarding the freshwater community and its response to human
disturbance of the watershed ecosystem.

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

The dynamic nature of the gut system is such that periodic visits should be frequent enough
to detect within season variations. Weekly site visits should be conducted to determine how
rainfall, evaporation, and flow affect species persistence and response. Although guts with
persistent pools are relatively rare in the USVI, sampling should be extended to include
more guts within more watersheds to eliminate bias of single disturbance events (such as the
sewage outflow in Dorothea and the upland development at Neltjeberg). Sediment levels in
gut pools should be systematically measured. Laboratory studies should be conducted to
determine species response to contaminants and to non-native species. Gut sampling should
also be extended to include insect fauna.

In addition, while territorial conferences on non-point source pollution as well as numerous
marine outreach programs on the fragility of the marine environment have sought to educate
schoolchildren and the voting populous, the more cryptic freshwater gut environments are
largely unappreciated for their ecological value and their sensitivity to anthropogenic
factors. There is a great need for public education, including lawmakers, to ensure that
development and zoning can proceed in an environmentally-agreeable manner.

Nemeth & Platenberg (2007)

Diversity of freshwater fauna in St. Thomas gut streams

ACKNOWLEDGEMENTS

This study was funded in part by Water Resources Research Institute grant 2006VI73B from
the US Geological Survey through the University of the Virgin Islands. Rifca Mathurin and
Duvane Hodge assisted in field work and water testing. Gaboury Benoit (Yale School of
Forestry & Environmental Studies) provided the continuous water quality data in Neltjeberg.
TKN and TP tests were performed by Kevin Brown at UVI's Center for Marine and
Environmental Studies. Additional support was provided through US Fish and Wildlife
Service Pittman-Robertson grant W-22 Wetland Conservation of St. Thomas and St. John
through the VI Division of Fish and Wildlife. All photos taken by R. Platenberg and D.
Nemeth.

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